The present invention relates to a brake disc, in particular for a motor vehicle, with a bowl-shaped brake-disc chamber having a wall region and a bottom region, and with a disc-shaped friction ring surrounding said brake-disc chamber coaxially with respect to a common mid-axis.
Brake discs of this type are known and are used as a component of brake systems, in particular in motor vehicles for racing. In this context, a friction ring consisting of carbon-fibre-reinforced carbon material (C/C) is connected by means of a number of connecting elements to a brake-disc chamber made of solid steel. The connecting elements, consisting of screws, spacer sleeves, nuts, sliding blocks, washers and the like, serve for transmitting torques which occur and for compensating the varying thermal expansion of the brake-disc chamber and the friction ring. This floating mounting avoids the friction ring being deformed (like an umbrella) and being subjected to mechanical stress by the brake-disc chamber which expands to a greater extent under heat. One disadvantage of this design is the high outlay in terms of cost which is caused by the multiplicity of connecting elements (for example, spacer sleeves or sliding blocks), sometimes difficult to produce, and which is taken into account in the construction of racing cars, but, for reasons of cost, cannot be allowed for in the mass manufacture of vehicles.
Furthermore, the advantage in terms of the weight of the friction-ring material C/C which can be achieved, as compared with conventional cast-iron brake discs, is cancelled again, at least in part, by the use of the many connecting elements and the solid, heavy brake-disc chamber.
German Patent Document No. DE-A 1 775 685 discloses a brake disc which consists of a hub part and of a brake ring and in which the brake ring and the disc hub have extensions and/or clearances which engage one into the other, the brake ring and hub being braced relative to one another by means of axially extending connecting elements, such as, for example, screws, rivets, bolts or the like. With this design, it is also considered necessary to use screws and rivets or bolts, with the result that the weight of the brake disc as a whole is increased.
German Patent Document No. DE 35 15 512 A1 discloses a friction ring, in particular for disc or drum brakes, which is produced entirely from ceramic. In order to achieve a rotationally fixed connection between the friction ring and brake housing in a drum brake using this friction ring, it is intended to provide the brake housing with concave projections on the inner circumference and the friction ring with convex recesses on the outer circumference, the projections and recesses engaging one into the other. For securing the two structural parts axially relative to one another, a flange is provided at the outer edge of the bowl-shaped hub, said flange having an annular groove, into which the friction ring extends. Designing the hub with a flange of this kind and introducing the friction ring with an exact fit into the annular groove of the flange must be considered as highly complicated.
U.S. Pat. No. Specification 5,007,508 discloses a brake-disc system, in which a brake disc has an inner fastening ring, on the inner circumference of which recesses are formed. The brake disc can be fastened to a brake-disc chamber in an axially floating manner. In order to ensure this fastening, quadrant pieces capable of being arranged in the recesses and, as bracing means, screws are provided. This arrangement has a multiplicity of individual parts and, for example due to the provision of screws for fastening the respective parts, has an increased weight.
The object of the present invention is, therefore, to provide a brake disc, in particular for a motor vehicle, which can be produced simply and cost-effectively from as few parts as possible and, at the same time, has as low a weight as possible.
This object is achieved by means of a brake disc characterized in that the friction ring has, on its inner circumference, clearances, into which projections formed on the wall region of the brake-disc chamber engage for the play-free transmission of a torque acting on the friction ring to the brake-disc chamber.
According to the invention, then, a brake disc is provided which has substantially fewer structural parts and a lower weight, as compared with conventional brake discs. The assembly outlay for fastening the friction ring to the brake-disc chamber is substantially lower than in the case of conventional brake discs, since no screw connections are provided. Clearances and projections can be dimensioned in a simple way, such that unimpeded radial and axial thermal expansion of the brake-disc chamber, manufactured, for example, from sheet metal, in relation to the friction ring is ensured and therefore a floating mounting of the friction ring is implemented.
Preferred refinements of the brake disc according to the invention are the subject-matter of the subclaims.
According to a preferred refinement of the brake disc according to the invention, elastically deformable parts are formed on the wall region of the brake-disc chamber in order to secure the friction ring axially in relation to the brake-disc chamber. Parts of this kind can be shaped in a simple way, for example by means of stamping, out of the wall region of the brake-disc chamber. In this case, it is possible in a simple way to provide desired axial play (with respect to the common mid-axis) between the brake-disc chamber and the friction ring. With deformable parts of this kind being produced, additional axial securing means, for example screws or bolts, can be dispensed with.
Expediently, the projections and the parts take the form of tabs which are produced by means of stamping or cutting and subsequent bending-round from portions of the wall of the brake-disc chamber. Tabs of this kind can be produced in a very cost-effective and simple way. Axial securing therefore takes place merely by the reshaping of tabs which are shaped out of the wall of the brake-disc chamber.
According to a further preferred refinement, the clearances formed in the friction ring have slot-like prolongations in their bottom region. When the projections or tabs engage into these slot-like prolongations, particularly effective torque transmission between the friction ring and brake-disc chamber can be achieved. This is because the necessary freedom of play between the tabs and the corresponding clearances of the friction ring can be produced in a very simple way, since the width of the prolongations (slot width) can be selected according to the low-tolerance sheet-metal thickness of the tabs. The unimpeded radial expansion of the tabs under heating is ensured here, too, by the prolongations being made somewhat longer in the radial direction than the tabs engaging into them.
According to a further preferred embodiment, the projections take the form of a toothed profile pressed into the wall region of the brake-disc chamber. A toothed profile of this kind, which has, in particular, rectangularly shaped teeth, can be pressed in a simple way into the wall region of the brake-disc chamber, with out the mechanical stability of said brake-disc chamber being impaired.
Expediently, the friction ring is secured axially on the brake-disc chamber by means of protrusions or pressed-out portions pressed into the wall region of the brake-disc chamber below and/or above the toothed profile. By virtue of this measure, the extent of axial play between brake-disc chamber and friction ring can be selected in a simple way. Here, too, the friction ring is secured axially on the brake-disc chamber merely by portions of the wall of said brake-disc chamber being reshaped into protrusions.
Advantageously, the friction ring is produced from a non-metallic material and the brake-disc chamber from a metallic material. Preferred materials for the friction ring are carbon-fibre-reinforced carbon materials (C/C) or fibre-reinforced composite ceramics based on silicon carbide (C/Cxe2x80x94SiC). Materials of this kind are substantially lighter than, for example, conventional cast-iron alloys. The brake-disc chamber preferably consists of Nirosta steel sheet which has a relatively low weight along with good mechanical stability.